1. Field of the Invention
The present invention relates to a suspension system for an automobile, in particular, to a suspension system for an automobile having a torsion bar.
2. Description of the Related Art
Japanese Utility Model Publication No. 61-27287 discloses a suspension system having a torsion bar which is twisted to urge a suspension arm when a load is applied to the arm in a substantially vertical direction of an automobile body, and which is allowed to move in a substantially front to rear or longitudinal direction of the body. This related art reference will hereinafter be referred to as the first related art reference. In this front suspension system, a front end of the torsion bar is mounted at the center of the rotation of a lower arm. In addition, a cross member is provided with a proximal end of an anchor arm which is made of a spring plate and extends in a substantially lateral direction of the body. The rear end of the torsion bar is fixed to a distal end of the anchor arm. Thus, when a load is applied to the suspension system in the substantially front to rear direction of the body, the anchor arm made of the spring plate elastically deforms, thereby moving the torsion bar and the lower arm in the substantially longitudinal direction of the body. Therefore, the riding comfort of the automobile is improved.
When a load is applied to the suspension system of this type, it is necessary to prevent the rear end of the torsion bar from directly contacting the cross member. Otherwise, the load will be transmitted from the torsion bar to the automobile body through the cross member. Thus, the riding comfort will be degraded. Therefore, in the suspension system disclosed in the first related art reference, the rear end of the torsion bar is provided with a rubber bushing so as to prevent the torsion bar from directly contacting the cross member.
However, when a load is applied to the suspension system in the substantially longitudinal direction of the body, a large reaction force takes place on the rubber bushing and thereby the rubber bushing is excessively worn. Therefore, the rubber bushing should have high durability. Nevertheless, if the rubber bushing is made of relatively hard rubber, the durability may be satisfied. However, the load will be transmitted to the body through the rubber bushing and the cross member, thereby degrading the riding comfort.
Another suspension system which is allowed to move in the substantially longitudinal direction of the body is disclosed in Japanese Patent Application Laid-Open No. 57-110514. This related art reference will hereinafter be referred to as the second related art reference. In this front suspension system, a lower arm is rotatably supported to the body at one position thereof. One end of a spring plate is fixed to the lower arm, whereas the other end of the spring plate is fixed to a front end of a torsion bar. Thus, when a load is applied to the suspension system in the substantially front to rear direction of the body, the spring plate elastically deforms and the lower arm moves in the substantially front to rear direction of the body, thereby improving the riding comfort of the automobile.
The construction of such a suspension system does not have enough rigidity against a load which is applied in the lateral direction of the body of the automobile. Thus, a bending force may be applied to the torsion bar. In the suspension system disclosed in the second related art reference, to prevent such a bending force from being applied to the torsion bar, the vicinity of a front end of the torsion bar is supported to a front end of a support member extending from the cross member by a bushing. In addition, a portion extending from the middle to the rear end of the torsion bar is movably supported by a cylindrical member which is supported by the cross member. Thus, this suspension system prevents a bending force from being applied to the torsion bar, thereby improving the rigidity in the lateral direction of the body of the automobile.
However, although the support member and the cylindrical member may prevent a bending force from being applied to the torsion bar, they will complicate the construction of the suspension system. Thus, such a suspension system is difficult to practically use.
In Japanese Patent Application Laid-Open No. 62-101507, a further suspension system is disclosed. This related art reference will hereinafter be referred to as the third related art reference. In this suspension system, a torsion bar is supported by a lower arm at a plurality of positions thereof so as to prevent a bending force from being applied to the torsion bar. However, in the third related art reference, the mounting construction of the lower arm and the torsion bar will become complicated.